1. Field of the Invention
This invention relates to the preparation of copolyamides and is particularly concerned with aromatic-aliphatic copolyamides.
2. Description of the Prior Art
Various types of polyamide polymers are known to those skilled in the art, see for example The Encyclopedia of Polymer Science and Technology, Vol. 10, pp. 347-593, 1969, Interscience Publishers, New York, N.Y. The various kinds of repeating units disclosed therein which are linked by the carbonamide group ##STR2## determine the variation in physical properties observed for the different types of polyamides. Physical properties like melting point and solubility are almost solely dependent on the type of repeating unit employed. For example, when all the repeating units are aromatic the polyamide has such a high melting point that melt processability, such as injection molding, is precluded because polymer decomposition begins to occur before the melt stage is ever reached.
Alternatively, when the repeating units are mixed aliphatic-aromatic, as in the case of a polyamide prepared from an aliphatic dicarboxylic acid and an aromatic diamine, the polymer is injection-moldable but because of high crystallinity is brittle, opaque, and possessed of low elongation. In fact, when the dicarboxylic acid component is either adipic, pimelic or suberic acid and the aromatic diamine is 4,4'-methylenedianiline the corresponding polyamides have decomposition temperatures below their melting points. This behaviour precludes melt processing these polymers; see J. Polymer Sci. 10, Part A-1, p. 1547, 1972. Finally, when the repeating units are all aliphatic as in nylon-6,6, the polymer is injection moldable but is limited in the end-use temperature to which it can be exposed.
The prior art discloses methods for the preparation of copolyamides derived from the reaction of mixtures of aliphatic dicarboxylic acids with aromatic dicarboxylic acids and aromatic diamines, or aromatic diisocyanates in either catalyzed melt condensation, solvent-interfacial condensation, or polar solvent condensation, as set forth in U.S. Pat. Nos. 3,408,334, 3,640,970, and 3,642,715 respectively.
Further, it is noted that mixtures of aliphatic dicarboxylic acids with minor amounts of aromatic dicarboxylic acids have been recognized as useful in the formation of copolyamides from bis(4-aminocyclohexyl)-methane (PACM), particularly in reference to the preparation of fibers as disclosed in U.S. Pat. No. 3,416,302. Broad ranges of mixtures of aromatic and aliphatic dicarboxylic acids have been reacted with meta-xylylenediamine (and mixtures of at least 50 percent meta-with para-xylylenediamine) and mixtures of xylylenediamines with aliphatic diamines to produce transparent injection moldable polyamides; see Netherlands specification Nos. 7212060 and 7304471.
The prior art does not disclose a polyamide composition which is easily injection molded and at the same time characterized by a higher end-use temperature as compared with aliphatic polyamides, and in possession of high impact strengths.
The copolyamides prepared in accordance with the present invention meet the above requirements and, furthermore, are characterized by unexpectedly high impact strengths.